Existing regulations specify a total amount of exposure to RF energy, above a threshold power density, that a user of a wireless terminal can be exposed to within a predetermined interval of time (e.g., averaged over one half hour).
One technique to determine the user's exposure would be to monitor the radiated power within the user's terminal and average over time the radiated power that exceeds the threshold. If the threshold level is exceeded within the specified interval of time, the user terminal could be rendered inoperable, thereby removing the user from the transmitted RF energy.
However, this approach could result in user terminals being modified or manufactured so as to defeat this function. Although the convenience to the user of always having the terminal available for use could be assured, the user may be exposed to relatively high levels of RF energy. Furthermore, a user terminal that is manufactured to operate with a specified allowable average power density could be rendered obsolete if the threshold level is later changed. As such, providing this function in the user terminal has a number of drawbacks.
Some user terminals are capable of operating with both a wireless terrestrial communications system as well as with the satellite communications system. In this case it can be appreciated that the user may experience, during a given period of time, different amounts of RF exposure in each system. These exposures may be cumulative if they occur within some predetermined period of time, such as when the user makes a call on the terrestrial system and then makes a call using the satellite system. However, at present there is no known mechanism for accounting for the user's RF exposure in each system.